Cardano MCP Transactions

cardano-mcp-transactions

Sign and submit pre-built unsigned transactions through a configured cardano MCP server. This is a high-risk operation — the MCP server has no server-side approval gate and will sign+submit any CBOR passed to it. Safety depends entirely on the preview-confirm flow defined below.

When to use

• User has a pre-built unsigned transaction (CBOR hex) from a dApp API, MeshTxBuilder, or cardano-cli transaction build.
• User wants to sign and submit that transaction via their MCP-configured wallet.
• A configured cardano MCP server is available.

When NOT to use

• User needs to build a transaction — use cardano-cli-transactions, meshjs-cardano, or koios-agent-wallet. The MCP server cannot construct transactions.
• No cardano MCP server is configured — use koios-agent-wallet (sign-submit mode) or cardano-cli transaction sign + submit.
• User needs testnet submission — current integration assumes mainnet unless testnet support is explicitly validated.
• The transaction CBOR cannot be summarized — refuse to submit (see operating rules).

Operating rules (MUST follow — no exceptions)

Rule 1: Never submit without a structured preview

Before calling submit_transaction, you MUST present a structured preview to the user containing ALL of the following fields:

=== Transaction Preview ===
Network:        mainnet (assumed)
Source wallet:  addr1qx... (from get_addresses)
Outputs:
  1. addr1qy... — 50.000000 ₳
  2. addr1qz... — 10.000000 ₳ + 100 HOSKY
Fee:            ~0.18 ₳
CBOR fingerprint: <first 16 hex chars>...<last 16 hex chars> (<total bytes> bytes)

Submit this transaction? (yes/no)

If you cannot produce this preview (e.g., you cannot decode the CBOR, or the transaction structure is opaque), you MUST refuse to submit and explain why.

Rule 2: Require unambiguous confirmation

The user must respond with a clear affirmative tied to the preview. Accept: "yes", "confirm", "submit it", "go ahead". Reject: vague responses like "sure", "whatever", "I guess", or any response that doesn't clearly reference the transaction. If ambiguous, ask again.

Rule 3: One transaction per confirmation

Each submit_transaction call requires its own preview-confirm cycle. Never batch or auto-submit.

Rule 4: Fail closed on uncertainty

• Cannot determine the network? Refuse.
• Cannot decode the CBOR? Refuse.
• Cannot identify the source wallet? Refuse.
• Unsure if MCP is configured for the right network? Refuse.

State what you cannot verify and suggest the user use CLI or Koios skills with explicit network flags instead.

Rule 5: Never ask for seed phrases or keys

The MCP server handles signing internally. Never prompt for mnemonics, private keys, or signing keys.

Rule 6: Network assumption

Current integration assumes mainnet unless testnet support is explicitly validated against the configured MCP server. If the user states they are on testnet, do NOT use this skill — route to koios-agent-wallet or cardano-cli-transactions-operator with explicit network flags.

MCP tool

submit_transaction

Sign and submit an unsigned transaction from the connected wallet.

• Input: { cbor: string } — unsigned transaction CBOR hex
• Output: { transactionHash: string, timestamp: number }
• Error: { content: [{ type: "text", text: "Unable to submit transaction : <error>" }] }
• The MCP server signs locally using the configured wallet's seed phrase (Lucid fromTx().sign.withWallet())
• There is no server-side approval gate — any valid CBOR will be signed and broadcast

Transaction sources

The MCP server cannot build transactions. The unsigned CBOR must come from elsewhere:

Provider precedence for signing+submit

Transaction submission:
  1. cardano MCP (if configured + preview confirmed) ← this skill
  2. koios-agent-wallet MODE=sign-submit (key-based, any network)
  3. cardano-cli transaction sign + submit (CLI, any network)

Unsupported or uncertain network → fail closed, do not silently switch providers.

Trust model

The seed phrase never leaves the MCP server process. The agent never sees key material. Safety depends on the preview-confirm flow in this skill and the user's own review.

References

• shared/mcp-provider.md
• shared/PRINCIPLES.md
• cardano-cli-transactions (CLI tx building guidance)
• cardano-cli-transactions-operator (CLI tx execution)
• koios-agent-wallet (Koios sign+submit)
• meshjs-cardano (MeshJS tx building)
• cardano-mcp: https://github.com/IndigoProtocol/cardano-mcp